Schooling, heritability and IQ

In recent recent weeks, in the UK, there has been renewed interest in the question of heritability and educational performance, after Dominic Cummings, the outgoing advisor to Michael Gove, the education secretary, claimed that some sort of left wing conspiracy in the educational establishment – “the blob” as Cummings calls it – were resisting the facts of science over the issue.

Tory house journal The Spectator joined in the debate, publishing a piece by psychology lecturer Kathryn Asbury which talks of a “genetically sensitive school”. I don’t know about you but that sounds like nothing good to me.

Psychometricians have by and large settled on a figure of 50 per cent for heritability based on what is now seen as a simplistic calculation that variance in a given environment for a trait – such as IQ – equals the sum of genetic and environmental contributions, plus a small component for the interaction of these two inputs. Robert Plomin, Gove’s behavioural genetics advisor and a prominent spokesman for this long psychometric tradition, puts it higher, at around 70 per cent, the figure cited by Cummings.

However, the calculation is almost meaningless. It depends on there being a uniform environment – fine if you are studying crop or milk yields, where you can control the environment and for which the measure was originally derived, but pretty useless when human environments vary so much. Thus some studies give a heritability estimate of 70 per cent for children in middle class families, but less than 10 per cent for those from poor families, where the environment is presumably less stable. And it is a changing environment, rather than changing genes, which must account for the increase in average IQ scores across the developed world by 15 points over the past century, to the puzzlement of the determinists.